Transmission Control Protocol/Internet Protocol (TCP/IP) is a connection-oriented,
Internet-standard, routable protocol in use on a majority of networks, including
the Internet. The protocol suite supports connectivity across a number of dissimilar
platforms and supports the main workload of most enterprises today that are
designed in a client/server configuration.

Some subtle changes have been incorporated into the TCP/IP suite for Windows
Server 2003. Internet Group Management Protocol (IGMP) version 3 adds support
for source-based filtering and reporting while maintaining backward-compatibility
with version 2. You can also use other settings so that systems can be configured
to use an alternate, manually configured IP address instead of one that a Dynamic
Host Configuration Protocol (DHCP) server provides. Autoconfiguration of the
enabled network interface card (NIC) metric is also available; this feature
determines the best routing metric for each interface's default gateway,
based on its speed. Support for TCP/IP version 6 has also been added in Windows
Server 2003.

These are some of the TCP/IP features that have been carried over from Windows
2000 Server:

Automatic Private IP Addressing (APIPA), which allows clients to assign
themselves a random IP address in the 169.254.0.0/16 range via subnet broadcast
when they are configured to use DHCP and no server is available

Quality of Service (QoS) mechanisms that reserve portions of the available
bandwidth, allowing it to be prioritized for time-sensitive applications
and transmissions

Virtual private networks (VPNs)

TCP scalable window sizes, including large TCP windows

Selective Acknowledgments (SACK)

Packet-level filtering

NetBIOS over TCP/IP (NetBT)

TCP/IP Protocol Suite

TCP/IP is a network communication protocol suite. It can be used as a
communications protocol on private networks and is the default protocol in use
on the Internet. When you set up any system to have direct access to the
Internet, whether it is via dial-up or a high-speed technology, your system
needs to use TCP/IP whether it is a Windows-based system or not.

Also, if systems need to communicate to other TCP/IP systems on the local
area network (LAN) or wide area network (WAN), they often use TCP/IP as
well.

NOTE

Indirectly connected computers, such as those on a LAN that connect to the
Internet via certain default gateways, certain types of routers, proxy servers,
or other indirect means, do not necessarily need to use TCP/IP. They need use
only the network protocol in use on the LAN, and that LAN protocol communicates
with the directly connecting mechanism (default gateway, router, proxy server,
or other direct device). That directly connected device needs to use the
Internet default protocol of TCP/IP.

For Internet Security and Acceleration (ISA) servers, systems must use TCP/IP
because it is the supported protocol for ISA.

TCP/IP is technically made up of two protocols. The upper layer, Transmission
Control Protocol, is responsible for breaking data down into smaller packets to
be transmitted over the network from a sending system (local and Internet), and
the TCP layer on the receiving system reassembles the packets it receives into
the original data structure. The lower layer, Internet Protocol, addresses each
packet so that it gets delivered to the correct remote system. Each routing
device on the network, be it a hardware router or a server system performing
routing functions, checks the destination address to see where to forward the
message.

The TCP/IP protocol suite maps to a four-layer conceptual model, which
parallels the seven-layer Open Systems Interconnect (OSI) protocol model
described in the following list:

Physical layerThis layer defines the interface between the
network medium (such as ethernet or token ring) and the hardware device (such as
a NIC). Multiplexers, hubs, and repeaters are just a few examples of the
components found at this layer of the OSI model.

Data Link layerThis layer is divided into two sublayers:
Logical Link Control (LLC), which handles error correction and flow control, and
Media Access Control (MAC), which handles communication with the NIC. Bridges
and switches are components that operate at this layer of the OSI
model.

Network layerThis layer translates logical network address
and names to MAC addresses for routing data packets over a network. A number of
protocols run at the Network layer, including IP, Address Resolution Protocol
(ARP), Reverse ARP (RARP), Internet Control Message Protocol (ICMP), Routing
Information Protocol (RIP), Open Shortest Path First (OSPF), IGMP, Internetwork
Packet Exchange (IPX), NWLink (the Microsoft version of the IPX/SPX protocol
suite), and NetBIOS Enhanced User Interface (NetBEUI). Brouters, routers, and
some types of ATM switches can be found at this layer of the OSI model.

Transport layerThis layer provides an additional connection
below the Session layer and assists with managing some data flow control between
hosts. Data is divided into packets on the sending node, and the receiving
node's Transport layer reassembles the message from packets. This layer is
also responsible for error checking to guarantee error-free data delivery, and
requests a retransmission if necessary. It is also responsible for sending
acknowledgments of successful transmissions back to the sending host. A number
of protocols run at the Transport layer, including TCP, ARP, RARP, Sequenced
Packet Exchange (SPX), and NWLink. Gateways and certain types of routers can be
found at this layer of the OSI model.

Session layerThis layer establishes, maintains, and ends
sessions between transmitting hosts and controls which host can transmit data at
a given interval and for how long. A number of protocols run at the Session
layer, including Named Pipes, NetBIOS Names, Remote Procedure Calls (RPC), and
Mail Slots. Gateways and certain types of proxy servers operate at this layer of
the OSI model.

Presentation layerThis layer translates data from the way
applications understand it to the way networks understand it. It is responsible
for protocol conversions, data encryption and decryption, and data compression
and decompression when the network is considered. Gateways and certain types of
redirectors operate at this layer of the OSI model. There are no protocols that
normally operate in this layer of the OSI model.

The four-layer conceptual model for the TCP/IP protocol suite is as follows:

Network Interface layerThis layer is responsible for putting
bits on the wire and correlates closely with the OSI model's Physical
layer and Data Link layer.

Internet layerThis layer is responsible for encapsulating
data packets into Internet datagrams. The Internet layer correlates, for
the most part, with the OSI model's Network layer. Four Internet protocols
operate at this layer:

IP supports connectionless packet delivery for all other protocols,
such as TCP or User Datagram Protocol (UDP). IP does not guarantee packet
arrival or correct packet sequence, nor does it acknowledge packet delivery.
These tasks are left to the application using the network or higher-level
protocols, such as TCP. IP is responsible for addressing and routing packets
only; error correction is left to the application or to higher-level protocols.

ARP is responsible for mapping IP addresses to physical machine addresses
called MAC addresses. IP broadcasts a special ARP inquiry packet containing
the destination system's IP address, and that system replies by sending
its physical address to the requester.

ICMP is charged with message control and error-reporting between network
hosts. Higher-level protocols use this information to recover from transmission
errors.

IGMP allows hosts to report their multicast group membership to multicast
routers. With multicasting, hosts can send multicast traffic to a single
MAC address, so multiple nodes can process the traffic.

TCP is a connection-oriented protocol that guarantees data delivery
by assigning a sequence number to each transmitted data segment so that
the receiving host can send an acknowledgment (ACK) to verify that the
data was received intact. If an ACK is not received or there was a transmission
error, the data is sent again.

UDP is a connectionless protocol that does not guarantee delivery or
correct sequencing of packets. Applications that use UDP are typically
tasked with the responsibility of ensuring data delivery because the protocol
does not. UDP is often used instead of TCP because of its lower overhead.
TFTP is an example of an application that uses UDP.

Application layerThis layer is where network-aware applications
operate. Network applications most commonly use two TCP/IP services, Winsock
and the NetBT interface.